This disclosure is in the field of reboiling a process fluid such as, but not limited to, those used in a distillation process.
The reboilers like those used in distillation process are heat exchangers to partially vaporize a process stream. There are different types of heat exchangers used as reboilers and multiple configurations of how the reboilers are connected with the distillation columns. Nevertheless, these reboilers run into scaling problems when the process fluid has the tendency to form scale due to its physical and chemical nature. Scaling is forming solids from a solution. Scaling in a reboiler is forming solids from the process fluid during partial vaporization.
U.S. Pat. No. 8,652,304 B2 (“Nazzer”) discloses a method of extracting dissolved or undissolved solids from a mixture of water and a process liquid or stream. This method lets the process fluid vaporize by directly contacting the heat transfer fluid, therefore eliminating the contact of process fluid on the heat exchanger which leads to scaling. In Nazzer's patent, the mixture is introduced into a mixing zone within or upstream of a separation vessel where it is further mixed with a recycle fluid extracted from a liquid pool zone of the separator vessel and pumped through a heat exchanger.
Vaporization occurs in this mixing zone (where more than 99% of the volatile components of the feed stream are vaporized). The resulting stream is then transferred to the separator vessel in which the vapor is separated, with the solid and liquid components falling into the liquid pool zone of the separator vessel. A portion of these solids and liquids that bond to these solids then passes through a stripping zone of the separator vessel. Water residing within the stripping zone displaces the liquids bound to the solids and an aqueous waste stream with dissolved or nondissolved solids results.
Because this method requires a mixing zone for vaporization outside of the liquid pool, the required equipment is difficult to design and prone to scaling and plugging. The method also does not allow for vaporization within the liquid pool and requires the heating medium—i.e., the recycle fluid, lighter than the water in the stripping zone—to be recycled at a rate of at least ten times that of the process feed rate. This high recycle rate is required because the method must limit the temperature difference between the recycle fluid and the process stream in order to avoid thermal degradation effects.
Last, the method requires a stripping zone for solids removal. A stripping zone is prone to corrosion because of unvaporized (solids) components from the process stream. The stripping zone also presents safety concerns due to the risk of higher temperature oil contacting water. To reduce the safety concern, the oil must be cooled before it touches the water in the stripping zone, but cooling the oil increases its viscosity and ineffective solids separation results. The stripping zone does not allow for partial vaporization in situations like a reboiler due to the mixing of the unvaporized process fluid with the water in the stripping zone.